1. Field of the Invention
The invention relates to a primary material utilized in making a metal mold used to mold a plastic. In embodiments, the mold is made of a high hardness material.
2. Discussion of Background information
Molds or matrices for producing or molding plastic parts require particular a homogenous material quality, especially over its cross section. Such molds will have essentially unchanging high quality characteristics during their entire service time or a planned number of parts or pieces produced thereby.
The most important properties that a primary material or a mold formed thereof can have relate to, on the one hand, a homogenous distribution of high material hardness, which resists abrasion, wear and permanent shape changes (especially in the work surface region), and, on the other hand, identical microstructures and a high degree of purity in the material. This latter feature is of specific concern during the machining of work surfaces, as well as polishing and/or chemical structuring of the same.
It is known from EP 1 251 187 B1, to utilize a tool steel for making molds used to mold plastic parts which have a composition that utilizes the following in weight of:    C=0.25-0.30    Si=0.04-0.20    Mn=1.20-2.00    Cr=1.00-2.00    Ni=0.90-1.50    Mo=0.30-0.80    V≦0.20    Al=0.01-0.03.
This material was created to form molds with high core hardness and a large diameter.
An Ni content of 0.90-1.50 percent by weight imparts to the material a continuous hardness which meets certain requirements during a tempering of the material, and without costly technical alloying measures, such as, for example, alloying with boron as well as aluminum and titanium—which is necessary to increase the hardness penetration depth.
However, a disadvantage relates to the fact that material hardness mainly above a value of 31 HRC (approximately 298 HB) cannot, or not with economic security, be achieved with high cost.